On December 2, 2014 5:31:13 AM EST, "Carlos E. R." robin.listas@telefonica.net wrote:
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On 2014-12-02 07:42, Achim Gratz wrote:
A snapshot is nothing more than telling btrfs "if anything writes to this file, make a copy of it and keep the old data around".
Which is not intuitive: typically a snapshot would be made at the instant of the request, occupying the full needed space. Btrfs snapshots are different, compact and fast. Not a backup snapshot.
I don't find snapshot a well-defined term. There are both COW snapshots and clone snapshots.
I believe most file systems use COW technology to implement snapshots. Linux LVM uses COW.
http://en.m.wikipedia.org/wiki/Snapshot_(computer_storage)#File_systems
But there are also lots of systems that implement snapshots as clones. The way I've seen the most is for a mirror to be created, then broken at snapshot time.
Greg